When starting a paper machine after a stoppage or a web break, the paper has to be passed through the machine again. Thus, from the edge of the paper web, a narrow edge strip is separated, which is first run through the machine. When the edge strip is made to travel through the machine or part of the machine, it can be spread to a full-width web. There are various guide systems available to make the edge strip follow the path of paper web travel formed by cylinders and rolls. Generally, in that case, rope systems, so-called threading ropes, are used, which travel outside the web egde, the tail being guided in between the ropes.
On-line threading of the edge strip with fast-running paper machines (the speeds typically over 20 m/s, design speeds at present even 30 m/s) is a problem, especially if the line involves processing devices which require complicated transfers. It is difficult to guide a fast moving tail along the correct path. Similarly, the fact that the tail tends to break when it hits obstacles during its travel, poses a problem.
In addition to the conventional rope transfer, attempts have been made to solve the problem with different belt support devices, air blows, suction devices, etc. These devices do help to achieve successful threading in relatively straightforward and simple transfers, but e.g. for an on-line multinip calender they do not provide an adequate solution.
Thus, the tail plays an important role in the beginning of the production run of the paper machine, and its transfer must proceed without disturbance. The tail itself should be strong enough to sustain the mechanical stresses of web feeding and not to break for example when hitting obstacles. Especially in the edge zone of the paper web, the strength of the web is a problem also in other respects, and thus, to strengthen the tail, Finnish patent 72550 suggests feeding of auxiliary pulp on the edge area of the paper web for strengthening the edge strip and also for reducing the tendency of the paper web to break in the production run. This requires changes in the feeding of the pulp in the headbox, or a particular device for feeding the auxiliary pulp.